Known in the art is an injection device supplying a hydraulic fluid from an accumulator to an injection cylinder and thereby driving a plunger connected to a piston of the injection cylinder and injecting the molding material into the mold by the plunger (for example Patent Literature 1 and 2). As the accumulator, in general, a gas pressure type which discharges the hydraulic fluid by utilizing the pressure of a compressed gas (for example air) has been utilized.
In the injection device in Patent Literature 1, in at least the latter half of the process of injecting the molding material into the mold (including boosting), the accumulator is kept in a state where the discharge of hydraulic fluid to the injection cylinder is permitted. Further, the injection cylinder is kept in a state allowing discharge of the hydraulic fluid in front of the piston along with forward movement of the piston. Accordingly, a final pressure (end pressure) of the molding material filled in the mold is determined according to the pressure of the accumulator. Therefore, Patent Literature 1 proposes a technique of discharging or filling the gas of the accumulator so that the required final pressure is suitably obtained.
In the injection device in Patent Literature 2, in order to make discharge or filling of gas of the accumulator as explained above unnecessary, the technique of prohibiting the discharge of the hydraulic fluid from the front of the piston along with the forward movement of the piston of the injection cylinder at a suitable timing has been proposed.